Many of the world's remaining natural gas reserves contain relatively high values of inerts, such as nitrogen gas and carbon dioxide. The presence of such inerts lowers the BTU value of the natural gas making it unsuitable as pipeline quality gas. In addition, the presence of both water and carbon dioxide may make the natural gas corrosive. In order to meet specifications for use such as pipeline quality specifications, these inerts must be wholly or substantially removed. Typical pipeline quality specifications mandate a total combined nitrogen and carbon dioxide content of less than about 6%.
Natural gas purification processes utilize numerous sub-processes which must be powered. For example, natural gas purification processes may include feed gas compression, recompression, sales gas compression, recycle gas compression, and various pumping processes. Moreover, inert removal processes generally utilize process equipment powered by electricity, including for example, heat tracing, instrumentation and controls, instrument air compression, dryers, and process plant lighting. These devices are generally operated utilizing either electric power from an existing electrical power distribution system or by an internal combustion engine powered by diesel or other appropriate fuel.
While electrically powered systems are generally reliable and require little maintenance, the cost of generating electrical power is rapidly increasing. Therefore, the cost of operating a large inert removal process or a large number of such processes which use electrically powered equipment (e.g., compressors) could be excessive or prohibitive. Moreover, many natural gas reserves are in remote locations at which utility electricity is not available. In such locations, the cost of supplying appropriate generator fuel could also be excessive or prohibitive.
Therefore, there exists a need for a power generation system which combines the economic advantages of a gas engine system with the relative reliability of electrical systems.